A liquid crystal display (LCD) device is a flat panel display widely used in a laptop or a cell phone at present. Due to the large market demand, the manufacturing process of the LCD device and a design of panel structures are continuously improved. For ensuring a display quality of the LCD, a light-on testing process is performed during the manufacture of a display panel, to determine whether pixels of the display panel can perform a normal operation. However, the conventional technology has a poor ability for testing the display panel.